A conventional four-stroke engine incorporates a large number of moving parts, which add to the engine's cost, weight, and complexity, while negatively impacting its reliability, serviceability, and longevity. Some parts that are associated with the valve train of a four-stroke engine are intake and exhaust valves of an engine include camshaft, camlobes, rockers, push tubes, rocker pins, reduction gears, and camshaft bearings. The intake and exhaust valves are each operated once every two rotations of the crankshaft, causing the camlobes mounted on camshaft to be rotated at half the engine-speed. This arrangement necessitates the use of a 1:2 reduction gear and a gear-train, thereby increasing the weight and parasitic losses of the engine. An increase in weight of any of the parts that constitute an engine, leads to a reduction in the engine's overall power-to-weight ratio.
Maximizing this power-to-weight ratio is very desirable in any engine design/construction. One method of improving this power-to-weight ratio may be carried out by reducing the weight of an existing part by the elimination of redundant parts by using alternative design approaches—for example. A second approach involves increasing the breathing efficiency of the engine by supercharging the engine using piston and crankcase as a pump. The combination of the first and second approaches becomes even more attractive when the replaced parts are moving parts, because a reduction in moving parts contributes to improved reliability of the engine.
As is known, when one moving part acts against another part, moving or stationary, friction is created thereby leading to generation of heat. Lubricating systems are typically used to reduce this heat. Lubricating systems related to four-stroke engines utilize oil as a lubricant. This oil is often stored in an oil reservoir from where it is drawn by a circulation system utilizing various mechanisms such as pumps, slingers, misters, and auxiliary reservoirs, to circulate the oil over the heat-generating moving parts. Some lubricating systems, such as those employed in engines for hand-held devices, place restrictions on the allowable orientation of this oil reservoir.
For example, certain trimmers cannot be operated upside down, because such an orientation causes the oil in the reservoir to be located at the wrong end of the reservoir where the pumping system cannot draw it out, or at the wrong end of the chamber where it cannot effectively lubricate the moving parts. While this orientation-issue has been addressed by a variety of solutions, some of the solutions have involved the use of complicated mechanisms incorporating a significant number of additional parts that add to the weight and complexity of the engine.
Besides the desirability of reducing the number of moving parts in an engine, and consequently reducing its lubricating requirements, it is also desirable that a lubricating system used in such an engine incorporates the least number of parts to perform its lubricating function while additionally permitting the engine to be operated in multiple orientations with good thermal efficiency. The thermal efficiency of an internal combustion engine is proportional to its expansion ratio. In a traditional engine this expansion ratio is typically equal to its compression ratio, thereby causing its thermal efficiency to be proportional to the compression ratio. Control of the compression ratio is limited by the characteristic of the fuel used in the engine, as the fuel determines when engine-knock occurs. This limitation may be overcome to some degree by operating the engine with a compression ratio that is lower than its expansion ratio. This operation can be generally carried out by adjusting the valve timing with reference to the piston's bottom-dead-center (BDC) either by closing the valve early before the piston reaches BDC during an intake stroke, or late after the piston passes BDC during a compression stroke. While this type of timing adjustment contributes to lowering the effective compression ratio, which may be described as a ratio of cylinder volume at BDC to the cylinder volume at intake valve closing, it also causes the effective displacement volume of the engine to be reduced thereby leading to an undesirable lowering of power density (power/cc of displacement), especially in naturally-aspirated engines. One solution to resolving the issue of reduced effective displacement volume involves turbo-charging. Unfortunately traditional turbo-charging techniques are expensive, and involve a number of additional engine parts.
Given the limitations of traditional internal combustion engines as described above, it is desirable to provide solutions that address such issues as improving the thermal efficiency, improving reliability, and reducing the number of parts, stationary or otherwise, that are used in the construction of internal combustion engines.